var arr1 = [['a', 1, true, 7], ['b', 2, false, 9]];
  // [[], [], [], []]
  //[['a', 'b'], [1, 2], [true, false], [7, 9]]
  var arr2 = [];

  for(let i = 0; i<arr1[0].length;i++){
    arr2.push([])
    for(let j = 0; j<arr1.length;j++){
      arr2[i].push(arr1[j][i])
    }
  }
  
console.log(arr2)